Surging that accompanies extreme pressure fluctuation and noise occurs in a low flow rate region in a centrifugal compressor used in a turbo compressor or a turbo refrigerator. When the centrifugal compressor is in a surging state, the compressor cannot stably operate and the life of the compressor is shortened. At worst, there is also a possibility that the compressor is damaged.
In view of it, various means for preventing the occurrence of surging were proposed in the past (for example, Patent Literatures 1 to 9).
Except for a particularly necessary case, the centrifugal compressor is abbreviated as the “compressor” and surging is abbreviated as “surge”.